September 24-28, 2007
Hyderabad, India

• What the high area-to-mass objects are?
• The research work goals and tasks
• Instruments involved into the high area-to-mass objects research program
• Overview of results
• Further steps in high area-to-mass objects population study

• Orbital objects having area-to-mass ratio more then 1 sq.m/kg (sometimes up to 100 sq.m/kg and more, i.e. 300 to 30000 times larger than for ‘normal’ spacecrafts and spent rocket bodies) we define as the high AMR objects
• Population of high AMR objects orbiting the Earth on so called GEO-like orbits is one of the most interesting targets for investigation in the recent years. They have orbital energy of the same order as usual representatives of GEO population that is an indicator of their genetic relation with ‘parent’ bodies on GEO
• Initially discovered by the AIUB team at the ESA Space Debris Telescope in their GEO and HEO surveys in 2003 and then confirmed by the ISON network leading by KIAM
• Similar objects have been found since that on ’classical’ HEO orbits as well
• These objects raised many questions as for their origin, nature, properties, orbital evolution and possibility of tracking on a regular basis.

• Search and detection of all unknown (uncatalogued) bright (brighter than 15.5^m) high objects and as maximal as possible number of faint high altitude objects on geocentric orbits for providing solid basis for construction of the most reliable picture of dynamical distribution of high near-Earth objects having size more than 15-20 cm
• Continuous tracking of detected objects
• Determination of trajectory parameters, estimation of area-to-mass ratio (AMR) for all tracked objects
• Analysis of orbital elements evolution and possible origin of tracked debris

• Since 2003 there are 91 high altitude object with AMR > 1 sq.m/kg discovered and continuously tracked during at least several nights
• 31 high altitude objects with AMR > 1 sq.m/kg discovered by the AIUB team in Teide and Zimmerwald 24 high altitude objects with AMR > 1 sq.m/kg discovered by the ISON facilities since 2005 are still continuously tracking at present
• Several dozens of just one-night track objects with period 1100-1600 min and non-zero eccentricity (first indication of possible high AMR) are discovered

• Due to their such physical properties high AMR objects have very strong orbital evolution that differs from other GEO and HEO population evolution. In particular, orbit eccentricity for continuously tracked GEO-like objects with AMR value of order of 30 sq.m/kg can vary between near 0 and 0.7 just in a half of year.
• Unknown attitude motion (supposedly tumbling) along with the high AMR value results in unpredictable variability of the SRP coefficient that in turn makes accurate motion determination and prediction for the most of this objects impossible for time intervals longer than just few days (in rare cases – 1-2 weeks) after the last observation obtained

• Many high AMR objects can be easily found even with small-class 22 cm instrument but…
• Objects are faint as a rule (17^m-18^m or fainter) for the most part of observation time and often have significant brightness variations at short time intervals thus making their observation problematic with small-class instruments and sometimes even with large aperture ones
• Objects shows very scattered pattern in brightness and sometimes weak dependence of brightness of a phase angle (at least within the range of observed phase angles). So it’s hard to estimate real size of such objects directly from optical observations.

Talking about high AMR objects on GEO-like orbits one can easily say that such objects are existing on all types of near-GEO orbits including librating and drifting ones. That means different originating mechanisms are involved into the high AMR object creation in that space region:
• for high AMR objects found on librating orbits → low velocity separation
• for high AMR objects found on drifting orbits → low velocity separation from objects on graveyard orbits or high velocity separation from any object in GEO region → additional minimal eccentricity analysis needed to understand the probable scenario

• Varying eccentricity results in large variation in distance from the object to observer that in turn adds additional problems:
  • Long variations of mean visible magnitude
  • Object becomes too faint on a large distance though slowly moving but too fast on closer path of orbit when the brightness is higher
• Variations of AMR value due to unpredictable attitude motion results in large prediction errors of the orbital motion even on short time intervals
• Due to high AMR the orbital motion is very ‘sensitive’ to shadow passes and in combination with attitude variations may result in additional uncertainty in orbital motion
• Resulted uncertainty in evolution makes the task of high AMR objects origin determination very hard
• Finally, strong eccentricity evolution results in constant change in the object distribution on high altitudes

• Special Action Item is established by the IADC for studying high AMR object physical properties
• Wide international cooperation of optical and radar facilities is involved into the research
• It is revealed that additional types of measurements (spectroscopy, simultaneous multicolor photometry etc.) should be obtained in order to understand origin of these objects
• Population of high AMR objects should be studied for other orbital regimes including HEO and LEO
• Improvement of the motion models